Method for making arcuate coil springs, resulting springs and devices for carrying out the method

ABSTRACT

The invention relates to a method for making arcuate coil springs from straight coil springs and particularly includes a phase of bending the straight springs during a heat treatment, which method provides exceptional results in that for the bending, a lasting arcuate shape is imparted to the springs substantially by giving the springs the shape of a portion of a turn to provide the spring with a counter-defect prior to the subsequent finishing steps. The invention also relates to a spring manufactured according to such a method and to devices for carrying out the method which include devices for holding at least the end coils of the springs in staggered positions, which devices may include a holder provided with fastening devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for making arcuate coil spring, theresulting springs and the necessary devices for carrying out thismethod.

2. Description of the Background Information

The arcuate coil springs are used in numerous mechanical systems which,in particular, require effects of returning and/or storing andrestituting energy, as is the case, for example, in the clutchingmechanisms referred to as "shock absorbing double flywheel", orautomatic transmissions, vehicle suspensions, etc.

It is known to manufacture such arcuate springs through methods thatconsist essentially of a deformation beyond the yield point of the coilsof the springs that are previously wound straight.

This deformation or bending is generally undertaken on the side whichwill constitute the external convex portion of the springs, by means ofconical or wedge pieces, which are introduced between the coils.

Of course, numerous operations are provided upstream and downstream ofthis bending operation.

Before bending, it is for example known to perform a straight winding ofthe coils, a tempering phase (so-called expansion), the grinding of theends, a prestress shot blasting of the straight springs, a heating andholding of close wound and hot coils.

In addition, after the aforementioned mechanical bending, the springsare hot stabilized, and are then scaled, i.e., controlled during torquein a given angular deformation, then possibly subjected to ananticorrosive treatment.

However, such a method has the disadvantage of causing marks on thesurface of the spring wire, due to the very bending operation, asmentioned. Such marks can constitute the beginning of rupture.

Variations of the aforementioned method can be brought in the order ofthe operations. Thus, the bending performed in the aforementionedmanner, for example, can be undertaken right after the winding,tempering and grinding operations, and then followed by the heating,holding of close wound and hot coils, shot blasting and reheating, tofinish with the scaling and the possible anticorrosive coating.

However, while grinding after bending makes it possible to remove thetraces of said bending, the incipient rupture remains.

One has also envisioned to perform a bending of the straight springsduring a heat treatment, as described for example, in the documentsWO-A-9106785 or EP 0 584 474. In the latter document, the spring is hotpressed at the winding temperature.

However, regardless of the method mentioned hereinabove, particularly inview of a subsequent shot blasting operation, the springs do notmaintain a proper flatness (i.e., a proper flat contact of a generatingline of the arcuate spring on a plane) because of the stresses broughtby said shot blasting.

That is why the inventor has envisioned an original bending method, adifferent order of operations with, in addition, specific devices.

SUMMARY OF THE INVENTION

The method according to the invention, for making arcuate coil springsfrom straight coil springs and comprising in particular a phase ofbending said straight springs during a heat treatment, is remarkable inthat for the bending, a lasting arcuate shape is imparted to the springssubstantially by giving them the shape of portion of a turn to providethe spring with a counter-defect prior to the subsequent finishingsteps.

Quite advantageously, the heat treatment performed during bendingcorresponds to an expansion tempering operation, contrary to theaforementioned document EP 0 584 474, in particular.

Also advantageously, the lasting arcuate position of the springs isobtained by holding at least the end coils of said springs.

Such a method makes it possible, among others, to obtain a properflatness of the finished spring.

Preferably, the tempering temperature is of about 350 to 450° C., andthe position is maintained for about four to a hundred twenty minutes.

Of course, other operations are provided before and after bending. Thus,said bending operation, for example, is generally preceded by anoperation of grinding the end coils of the straight springs, andpossibly by a first operation of heating the straight springs at atemperature of about 180 to 220° C. for about twenty to forty minutes.

After bending, the following successive operations can be provided:prestress shot blasting, heating and holding close wound and hot coils,control of the scaling torques, which operations are possibly completedby an anticorrosive coating operation.

Of course, the invention also relates to an arcuate coil springmanufactured according to the aforementioned method.

To implement the method, the invention provides a device that ischaracterized in that it comprises means for holding at least the endcoils of the springs in staggered positions, substantially to give thespring the shape of a portion of a turn.

The device can have the form of a cylindrical annular box in which eachspring is introduced so that a lasting arcuate shape is imparted theretoover its entire length, or the form of a holder provided with fasteningmeans for the end coils of the springs.

According to an alternative embodiment, it can also have the form of anon-rectilinear pin whose ends are adapted to be introduced in the endcoils of the springs, or the form of a pin made of two parts, in whichthe ends on one side of said parts are adapted to be introduced in theend coils of the springs, while the other free ends can be connected toone another by a fastening member.

Preferably, the devices are metallic and thermally treated.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill be made apparent from the following description of the preferredembodiments, given as non-limiting examples, with reference to theaccompanying drawings in which:

FIG. 1 shows a top view of a device according to the invention, in theform of an annular box;

FIG. 2 is a cross-section along II--II of FIG. 1;

FIG. 3 shows another device in the form of a holder for the ends of thesprings;

FIG. 4 shows an embodiment in the form of a variation of FIG. 3;

FIG. 5 shows a device in the form of a non-rectilinear pin;

FIG. 6 shows a device in the form of a pin made of two distinct parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The complete and advantageous method according to the invention, afterthe winding of each straight spring, therefore consists of: grindingeach end of the spring, bending the spring, as will be explainedhereinafter, during the same tempering phase at a temperature comprisedbetween 350 and 450° C., and for a duration of four to a hundred twentyminutes, then undertaking a prestress shot blasting of the arcuatesprings in one or two operations, reheating at temperatures of about 180to 280° C., then holding the close wound springs (by compressing thearcuate spring) and at the aforementioned temperature, then controllingthe scaling torques and possibly, providing an anticorrosive coating.

As previously mentioned, a heating operation (or expansion tempering)can be performed at a temperature of 180 to 220° C. for about twenty toforty minutes before the bending operation, and more precisely betweenthe winding operation and the grinding operation.

The bending operation is therefore performed during the tempering phaseunder the aforementioned conditions, by imparting a lasting arcuateshape to the springs and, advantageously, by holding at least the endcoils of the springs.

To this end, a plurality of devices have been envisioned by theinventor, at least certain of which are shown in the drawings. Thesedevices are arranged to hold at least the ends of the springs with astaggering or misalignment of the latter.

FIGS. 1 and 2 show a first device D₁, in the form of a box constitutedby two concentric tubes 1a, 1b, connected to one another by a base 2(FIG. 2), and providing therebetween an annular space 3 adapted toreceive a spring R₁.

It is clear that the aforementioned annular space is calculated as afunction of the diameter of the springs to receive.

Each spring can be introduced from the top, when considering FIG. 2,which top can possibly be provided with a lid.

In order to create a counter-defect, as mentioned hereinabove, a wedge 4(FIG. 2), for example, can be provided so as to give the spring theshape of a portion of a turn.

The box or device D₁, shown is circular, but it could be oval.

The devices D₂ and D₃ of FIGS. 3 and 4 are holders provided withfastening means for the end coils of the springs which are referencedhere as R₂ and R₃.

The fastening means are, for example, constituted by parallel walls(they could be slightly oblique with respect to one another) such as 5a,5b; 6a, 6b (FIG. 3) and 8a, 8b; 9 (FIG. 4), between which the end coilor coils (two for example) are fastened as shown in the drawings.

In addition, for the device D₂, lateral walls 10a, 10b; 11a, 11b, areprovided, the whole extending here from a folded metal plate 7 possiblyprovided with a base 7'.

One can note that, as previously, a counter-defect is created by givinga shape of a turn to the spring, such as a turn of a helix (as apparentfrom viewing FIGS. 3 and 4), by staggering the ends, here by a value P₂for D₂ and P₃ for D₃. Furthermore, it can be noted that with the deviceD₂ of FIG. 3, the two ground ends of the spring R₂ create an angle "a"therebetween, that is a function of the desired geometry for the thespring, whereas in the device D₃ of FIG. 4, the ends of the spring R₃are parallel spring R₃ are parallel while in support on the same wall 9.

In FIG. 5, one can see a device D₄ in the form of a non-rectilinear pin,and whose shape is appropriate to provide the spring R₄ with the desiredshape (arcuate shape and shape of a turn).

The pin D₄ here has a square section while each end is adapted to befastened in one or two end coils of the spring R₄.

The pin D₄ thus exerts, on the ends of the spring R₄, a torque on one ortwo coils along an axis constituted by a diameter of the end coil.

The device D₅ of FIG. 6 for a spring R₅ is a pin made of two distinctparts 12, 13.

One of the ends of each part 12, 13, is adapted, as previously, toengage with one or two coils of the spring R₅, while the other ends areadapted to be connected to one another in a releasable manner by meansof a fastening member 14, which is here in the form of a single ring,such that the spring R₅, of the device D₅ can be easily installed andremoved.

This last device is more particularly adapted for springs that are shortand have a large radius of curvature.

To facilitate the positioning of the springs in the devices, anautomatic apparatus can be utilized to arcuate said springs, this devicecomprising, for example, a rotative jack that follows an evolute in theshape of a turn.

Of course, the aforementioned devices or tools must have the requiredresistance and dimensions to enable proper reproducibility of thefinished products, the latter being capable of being preferably made ofmetal with a good mechanical strength acquired through an adequate heattreatment.

It is also clear that the various parameters of the method describedhereinabove, as well as the dimensions and shapes of the devices for itsimplementation are determined as a function of the characteristics ofthe arcuate springs to obtain.

What is claimed is:
 1. A method for making arcuate coil springs fromstraight coil springs comprising:forming a straight coil spring duringheat treatment to have an arcuate shape; and providing the arcuateshaped spring with a counter-defect prior to subsequent finishing steps,wherein said counter-defect is formed by bending the arcuate shapedspring to result in a shape having a portion of a turn.
 2. The methodaccording to claim 1, wherein said heat treatment performed duringbending corresponds to an expansion tempering operation.
 3. The methodaccording to claim 2, wherein said tempering temperature is about 350 to450° C.
 4. The method according to claim 2, wherein said temperingoperation in the maintained position has a duration of about 4 to 120minutes.
 5. The method according to claim 1, wherein the bending ispreceded by grinding the end coils of the straight springs.
 6. Themethod according to claim 1, wherein the bending is preceded by a firstoperation of heating the straight spring.
 7. The method according toclaim 6, wherein said first heating operation is performed at atemperature of about 180 to 220° C. for about 20 to 40 minutes.
 8. Themethod according to claim 1, wherein said bending is completed by thefollowing successive operations: prestress shot blasting, heating andholding of close wound and hot coils, and control of scaling torques. 9.The method according to claim 8, wherein said method is completed by ananticorrosive coating operation.
 10. The method according to claim 1,further comprising: providing a holding device that holds the end coilat one end of the spring in a position offset from the end coil at theother end of the spring, such that the arcuate spring takes the shape ofa portion of a turn.
 11. The method according to claim 10, wherein saidholding device further comprises fastening elements for fastening theend coils of the spring.
 12. The method according to claim 10, whereinsaid holding device is configured as a non-rectilinear pin having endsadapted to be introduced into the end coils of the spring.
 13. Themethod according to claim 10, wherein said holding device is configuredas a pin formed from two parts, wherein the ends on one side of saidparts are adapted to be introduced into the end coils of the spring,while the free ends of said parts are adapted to be connected to oneanother by a fastening member.
 14. The method according to claim 10,wherein said holding device is metallic and is thermally treated. 15.The method according to claim 1, wherein said counter-defect imparted tothe arcuate shaped spring is obtained by holding at least the end coilsof said arcuate shaped spring.
 16. A method for making arcuate coilsprings from straight coil springs comprising:forming a straight coilspring during heat treatment to have an arcuate shape; and providing thearcuate shaped spring with a counter-defect prior to subsequentfinishing steps, wherein said counter-defect is formed by bending thearcuate shaped spring to result in a shape having a portion of a turn,and a device for carrying out the method comprising: a holding devicethat holds the end coil at one end of the spring in a position offsetfrom the end coil at the other end of the spring, such that the arcuatespring takes the shape of a portion of a turn, and wherein said holdingdevice is configured in the form of a cylindrical annular box forreceiving a spring, such that a lasting arcuate shape is impartedthereto over the entire length thereof, and further comprising amechanism positioned within said cylindrical annular box to ensure theoffsetting of at least the end coils of the spring.